A halogen-containing resin is unstable with regard to heat or light. Therefore, it is necessary to incorporate a thermal stabilizer before thermal melting and molding. Metal soaps such as Cd/Ba, Ba/Zn and Ca/Zn, lead stabilizers, tin stabilizers and hydrotalcites are used as the thermal stabilizer. However, the use of a toxic stabilizer is gradually limited or prohibited in recent years. The use of stabilizers containing Cd and Pb and additionally Ba is rapidly decreased. Hydrotalcites and Ca/Zn-containing stabilizers are widely used in place of the above stabilizers. Tin stabilizers are used since the toxicity thereof is less than that of Cd or Pb. However, when a hydrotalcite is used for an electric cable, in particular for a highly heat-resistant electric cable, it is required to incorporate the hydrotalcite in a large amount so that the mechanical strength or electric insulation of a halogen-containing resin is undesirably impaired. The tin stabilizers are in a liquid state so that a problem is that processing stability is poor or they decrease the softening point of a resin.
A complex of a metal silicate and a calcium hydroxide compound, which has been invented by the present inventor, (Japanese Patent Application No. 2007-52892) brings about an improvement in the initial coloration of a hard halogen-containing resin composition, which coloration is a defective of a calcium hydroxide compound, and also brings about an improvement in thermal stability.
However, with regard to a soft halogen-containing resin composition, for example, for a high heat-resistant electric cable, the thermal stability of the complex is almost the same as that of a hydrotalcite.
Therefore, it is required to incorporate the complex in a large amount so that the electric insulation or flexibility of the electric cable is largely reduced. For solving this problem, a higher-performance stabilizer, which can give intended stabilization even when incorporated in a smaller amount, is demanded.
On the other hand, calcium stearate is added as a lubricant for the purpose of improving processability in many cases In these cases, initial coloration becomes strong as compared with a case where calcium stearate is not added. Therefore, when the complex is incorporated even for uses other than electric cable, it is required to make a further improvement in terms of the initial coloration.